1. Field of the Invention
This invention relates to photothermographic materials that form color images upon light exposure and heat development. More specifically, this invention relates to hydrazide redox-dye-releasing ("RDR") compounds that are suitable for use in photothermographic imaging systems.
2. Background Art
Silver halide-containing, photothermographic imaging materials (i.e., heat-developable photographic elements) processed with heat, and without liquid development, have been known in the art for many years. These materials, also known as "dry silver" compositions or emulsions, generally comprise a support (also sometimes referred to as a substrate or film base) having coated thereon: (a) a photosensitive material that generates elemental silver when irradiated; (b) a non-photosensitive, reducible silver source; (c) a reducing agent for the non-photosensitive, reducible silver source; and (d) a binder. Thus, photothermographic systems are distinct from conventional wet silver photographic systems due to the presence of the non-photosensitive, reducible silver source and the reducing agent for this silver source.
The photosensitive material is generally photographic silver halide that must be in catalytic proximity to the non-photosensitive, reducible silver source. Catalytic proximity requires an intimate physical association of these two materials so that when silver atoms (also known as silver specks, clusters, or nuclei) are generated by irradiation or light exposure of the photographic silver halide, those nuclei are able to catalyze the reduction of the reducible silver source. It has long been understood that silver atoms (Ag.degree.) are a catalyst for the reduction of silver ions, and that the photosensitive silver halide can be placed into catalytic proximity with the non-photosensitive, reducible silver source in a number of different fashions. For example, catalytic proximity can be accomplished by partial metathesis of the reducible silver source with a halogen-containing source (see, for example, U.S. Pat. No. 3,457,075); by coprecipitation of silver halide and the reducible silver source material (see, for example, U.S. Pat. No. 3,839,049); and by other methods that intimately associate the photosensitive photographic silver halide and the non-photosensitive, reducible silver source.
The non-photosensitive, reducible silver source is a material that contains silver ions. Typically, the preferred non-photosensitive, reducible silver source is a silver salt of a long chain aliphatic carboxylic acid having from 10 to 30 carbon atoms. The silver salt of behenic acid or mixtures of acids of similar molecular weight are generally used. Salts of other organic acids or other organic materials, such as silver imidazolates, have also been proposed. U.S. Pat. No. 4,260,677 discloses the use of complexes of inorganic or organic silver salts as non-photosensitive, reducible silver sources.
In photothermographic emulsions, exposure of the photosensitive material, e.g., photographic silver halide, to light produces small clusters of silver atoms (Ag.degree.). The imagewise distribution of these clusters is known in the art as a latent image. This latent image is generally not visible by ordinary means. Thus, the photosensitive emulsion must be further processed in order to produce a visible image. The visible image is produced by the reduction of silver ions, which are in the non-photosensitive, reducible silver source and in catalytic proximity to silver halide grains bearing the clusters of silver atoms, i.e., the latent image.
The reducing agent for the non-photosensitive, reducible silver source, is often referred to as a "developer." It can be any material, preferably any organic material, that can reduce silver ions to metallic silver. At elevated temperatures, in the presence of the latent image, the non-photosensitive, reducible silver source (e.g., silver behenate) is reduced by this reducing agent to form a negative black-and-white image of elemental silver.
While conventional photographic developers such as methyl gallate, hydroquinone, substituted-hydroquinones, hindered phenols, catechol, pyrogallol, ascorbic acid, and ascorbic acid derivatives are useful, they tend to result in very reactive photothermographic formulations and fog during preparation and coating of the photothermographic element. As a result, hindered bisphenol reducing agents have traditionally been preferred although a wide range of reducing agents have been disclosed in dry silver systems. These include amidoximes, such as phenylamidoxime, 2-thienylamidoxime and p-phenoxy-phenylamidoxime; azines, such as 4-hydroxy-3,5-dimethoxybenzaldehydeazine; a combination of aliphatic carboxylic acid aryl hydrazides and ascorbic acid, such as 2,2'-bis(hydroxymethyl)propionyl-.beta.-phenylhydrazide in combination with ascorbic acid; a combination of polyhydroxybenzene and hydroxylamine; a reductone and/or a hydrazine, such as a combination of hydroquinone and bis(ethoxyethyl)hydroxylamine, piperidinohexose reductone, or formyl-4-methylphenylhydrazine; hydroxamic acids, such as phenylhydroxamic acid, p-hydroxyphenylhydroxamic acid, and o-alaninehydroxamic acid; a combination of azines and sulfonamidophenols, such as phenothiazine with p-benzenesulfonamidophenol or 2,6-dichloro-4-benzenesulfonamidophenol; .alpha.-cyanophenylacetic acid derivatives, such as ethyl .alpha.-cyano-2-methylphenylacetate, ethyl .alpha.-cyano-phenylacetate; bis-o-naphthols, such as by 2,2'-dihydroxyl-1-binaphthyl, 6,6'-dibromo-2,2'-dihydroxy-1,1'-binaphthyl, and bis(2-hydroxy- 1-naphthyl)methane; a combination of bis-o-naphthol and a 1,3-dihydroxybenzene derivative, such as 2,4-dihydroxybenzophenone or 2,4-dihydroxyacetophenone; 5-pyrazolones such as 3-methyl-1-phenyl-5-pyrazolone; reductones, such as dimethylaminohexose reductone, anhydrodihydroaminohexose reductone, and anhydrodihydro-piperidone-hexose reductone; sulfonamidophemol reducing agents, such as 2,6-dichloro-4-benzenesulfonamidophenol and p-benzenesulfonamidophenol; indane-1,3-diones, such as 2-phenylindane-1,3-dione; chromans, such as 2,2-dimethyl-7-t-butyl-6-hydroxychroman; 1,4-dihydropyridines, such as 2,6-dimethoxy-3,5-dicarbethoxy-1,4-dihydropyridine; bisphenols, such as bis(2-hydroxy-3-t-butyl-5-methylphenyl)methane, 1,1-bis(2-hydroxy-3,5-dimethylphenyl)-3,5,5-trimethylhexane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 4,4-ethylidene-bis(2-t-butyl-6-methylphenol), and 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane; ascorbic acid derivatives, such as 1-ascorbylpalmitate, ascorbylstearate; unsaturated aldehydes and ketones; certain 1,3-indanediones; and 3-pyrazolidinones such as 1-phenyl-3-pyrazolidinone (phenidone) as described in Research Disclosure, June 1978, item 17029, and biphenyls such as 2,2'-dihydroxy-3,3'-di-t-butyl-5,5'-dimethylbiphenyl as described in European Laid Open Patent Application No 0 509 740 A1.
As the visible image in black-and-white photothermographic elements is produced entirely by silver atoms (Ag.degree.), one cannot readily decrease the amount of silver in the emulsion without reducing the maximum image density. However, reduction of the amount of silver is often desirable to reduce the cost of raw materials used in the emulsion and/or to enhance performance. For example, toning agents can be incorporated to improve the color of the silver image of the photothermographic element. Another method of increasing the maximum image density in photographic and photothermographic emulsions without increasing the amount of silver in the emulsion layer is by incorporating dye-forming materials in the emulsion. Upon imaging, the leuco dye is oxidized, and a dye and a reduced silver image are simultaneously formed in the exposed region. In this way, a dye-enhanced silver image can be produced.
A number of methods have been proposed for obtaining color images with dry silver systems. Such methods include, for example, incorporating dye-forming coupler materials into the dry silver systems. Known color-forming dry silver systems include: a combination of silver benzotriazole, a magenta, yellow, or cyan dye-forming coupler, an aminophenol developing agent, a base release agent such as guanidinium trichloroacetate, and silver bromide in polyvinyl butyral; and a combination of silver bromoiodide, sulfonamidophenol reducing agent, silver behenate, polyvinyl butyral, an amine such as n-octadecylamine, and 2-equivalent or 4-equivalent yellow, magenta or cyan dye-forming couplers.
Color images can also be formed by incorporation of dye forming or dye releasing compounds into the emulsion. Upon imaging, the dye forming or dye releasing material is oxidized and a dye and a reduced silver image are simultaneously formed in the exposed region.
U.S. Pat. No. 4,021,240 discloses the use of sulfonamidophenol reducing agents and four equivalent photographic color couplers in photothermographic emulsions to produce dye images. U.S. Pat. No. 3,531,286 discloses the use of photographic phenolic or active methylene color couplers in photothermographic emulsions containing p-phenylenediamine developing agents to produce dye images. U.S. Pat. No. 4,463,079 discloses the use of sulfonamidophenol and sulfonamidonaphthol redox-dye-releasing compounds which release a diffusible dye on heat development. U.S. Pat. No. 4,474,867 discloses the use of dye-releasing couplers which, in combination with a reducing agent, release a diffusible dye on heat development. U.S. Pat. No. 4,981,775 discloses the use of redox-dye-releasing compounds, e.g., oxazines, thiazines, and azines, that release a diffusible dye on heat development.
Color images can also be formed by incorporation of leuco dyes into the emulsion. A leuco dye is the reduced form of a color-bearing dye. It is generally colorless or very lightly colored. Upon imaging, the leuco dye is oxidized, and a color-bearing dye and a reduced silver image are simultaneously formed in the exposed region. In this way, a dye-enhanced silver image can be produced. U.S. Pat. No. 4,022,617 discloses the use of leuco dyes in photothermographic emulsions. The leuco dyes are oxidized to form a color image during the heat development of the photothermographic element. Chromogenic leuco dyes having various protecting groups are described in U.S. Pat. No. 5,330,864 and in Applicant's Assignees copending application Ser. No. 08/161,900 (filed Dec. 3, 1993).
Multicolor photothermographic imaging elements typically comprise two or more monocolor-forming emulsion layers (often each emulsion layer comprises a set of bilayers containing the color-forming reactants) maintained distinct from each other by barrier layers. The barrier layer overlaying one photosensitive, photothermographic emulsion layer typically is insoluble in the solvent of the next photosensitive, photothermographic emulsion layer. Photothermographic elements having at least two or three distinct color-forming emulsion layers are disclosed in U.S. Pat. Nos. 4,021,240 and 4,460,681. Various methods to produce dye images and multicolor images with leuco dyes are well known in the art as represented by U.S. Pat. Nos. 4,022,617; 3,531,286; 3,180,731; 3,761,270; 4,460,681; 4,883,747; and Research Disclosure, March 1989, item 29963. Various other dye-releasing systems have been disclosed in U.S. Pat. Nos. 4,060,420; 4,731,321; 4,088,496; 4,511,650; and 4,499,180.
The imaging arts have long recognized the field of photothermography as being clearly distinct from that of photography. Photothermographic elements significantly differ from conventional silver halide photographic elements which require wet-processing.
In photothermographic imaging elements, a visible image is created by heat as a result of the reaction of a developer incorporated within the element. Heat is essential for development. Temperatures of over 100.degree. C. are routinely required. In contrast, conventional wet-processed photographic imaging elements require processing in aqueous processing baths to provide a visible image (e.g., developing and fixing baths). Development is usually performed at a more moderate temperature (e.g., 30.degree.-50.degree. C.).
In photothermographic elements only a small amount of silver halide is used to capture light. A different form of silver (i.e., the non-photosensitive, reducible silver source, such as silver behenate) is used to generate the image with heat. Thus, the silver halide serves as a catalyst for the development of the non-photosensitive, reducible silver source. In contrast, conventional wet-processed photographic elements use only one form of silver (e.g., silver halide) which, upon development, is converted to silver. Additionally, photothermographic elements require an amount of silver halide per unit area that is as little as one-hundredth of that used in a conventional wet-processed silver halide.
Photothermographic systems employ a light-insensitive silver salt, such as silver behenate, which participates with the developer in developing the latent image. In contrast, photographic systems do not employ a light-insensitive silver salt in the image-forming process. As a result, the image in photothermographic elements is produced primarily by reduction of the light-insensitive silver source (silver behenate) while the image in photographic black-and-white elements is produced primarily by the silver halide. In photothermographic elements, the unexposed silver halide inherently remains after development. Thus, the element must be stabilized against further development. In contrast, the silver halide is removed from photographic elements after development to prevent further imaging (i.e., the fixing step).
In photothermographic elements a number of binders are useful, whereas photographic elements are limited almost exclusively to hydrophilic colloidal binders such as gelatin. Furthermore, in photothermographic elements, all of the "chemistry" of the system is incorporated within the element itself. For example, photothermographic elements incorporate a developer (i.e., a reducing agent for the non-photosensitive, reducible source of silver) within the element while conventional photographic elements do not. Even in instant photography, developer chemistry is physically separated from the silver halide until development is desired. The incorporation of the developer into photothermographic elements can lead to increased formation of "fog" upon coating of photothermographic emulsions as compared to photographic emulsions.
Because photothermographic elements require thermal processing, they pose different considerations and present distinctly different problems in manufacture and use. In addition, the effects of additives (e.g., stabilizers, antifoggants, speed enhancers, sensitizers, supersensitizers, etc.), which are intended to have a direct effect upon the imaging process, can vary depending upon whether they have been incorporated in a photothermographic element or incorporated in a photographic element.
Other distinctions between photothermographic and photographic elements are described in Imaging Processes and Materials (Neblette's Eighth Edition); J. Sturge et al. Ed; Van Nostrand Reinhold: New York, 1989; Chapter 9 and in Unconventional Imaging Processes; E. Brinckman et al, Ed; The Focal Press: London and New York: 1978; pp. 74-75.
Hydrazides have been used in conventional wet processed black-and-white and color photographic systems. They have found use as nucleating agents, infectious developers, contrast and speed improving agents, and color developing agents. U.S. Pat. No. 4,902,599 describes the combination of hydrazine and a hydrazide, and color image formation by a coupler-developer reaction.
Sulfonyl hydrazides have been used in traditional dye diffusion transfer instant photography. The decomposition of sulfonyl-hydrazides has been studied by H. Golz, et al., Angew. Chem. Int. Ed. Engl., 16(10), 728-729 (1977). Low temperature oxidation with lead tetraacetate leads to the azo compound which can then undergo further decomposition by loss of nitrogen.
G. J. Lestina, et al., Research Disclosure, December 1974, item 12832 describes the use of hydrazide dye-releasing compounds in color photography. Dye is released upon alkaline hydrolysis of the acylazo- or sulfonylazo compound generated upon exposure in the presence of AgX, a silver halide developer, and an electron transfer agent. U.S. Pat. No. 3,844,785 describes sulfonyl hydrazides as dye forming compounds in a dye diffusion transfer photographic process. U.S. Pat. No. 4,386,150 uses dyes attached to hydrazides including sulfonyl hydrazides in a construction for instant photography. This construction requires aqueous alkaline processing.
Japanese Laid Open Patent Publication No. JP 63-113455 describes the use of sulfonyl hydrazides attached to a pre-formed dye moiety in thermally developed photographic elements containing large amounts of photosensitive silver halide relative to non-photosensitive silver salts. Development of these materials takes place in a basic aqueous environment, however.
It is an object of the present invention to provide alternative heat developable color photographic materials capable of releasing dyes to provide clear, stable color images.